Running Ubuntu 11.04 (Natty) unity 3D on virtualbox 4.x
Unity has a vertical task management panel on the left-hand side and a menu panel at the top of the screen. Using a sidebar for task management conserves vertical screen space, which is much more valuable on a widescreen netbook. The task panel displays icons for commonly-used applications and programs that are currently running. Clicking on an icon will give the target application focus if it is already running or launch it if it is not already running. If you click the icon of an application that already has focus, Unity will activate an Expose-style view of all the open windows associated with that application.
Procedure to follow
1) Download and install virtualbox 4.x from here
2) Now you need to create new vitual machine after that open VM go to settings and click on display check "Enable 3D Acceleration" option
3) Download ubuntu 11.04 latest from here and install ubuntu 11.04
After completing the ubuntu 11.04 installation you need to install Virtualbox guest additions for this you need to click on Devices-->Installguest additions this wll start a VBoxLinuxAdditions.run script so you need to run this script when it is done close the terminal and restart yourubuntu 11.04 virtual machine.
Now your unity should be working and i am giving my unity screenshot under virtualbox as follows